1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus for image reading, such as a facsimile machine, an image scanner, a digital copy machine, etc., and to an image reading apparatus using the photoelectric conversion apparatus.
2. Description of the Related Art
In conventional facsimile machines, image scanners, digital copy machines or the like, a unit-magnification contact image sensor or a photoelectric conversion apparatus (image reading sensor) having a CCD (charge-coupled device) is used. In such a sensor, a plurality of chips each having a photoelectric conversion function are connected and arrayed in a scanning direction.
In a photoelectric conversion apparatus disclosed in Japanese Laid-Open Patent Application No. 10-191173, electric charge generated and stored in photoelectric conversion elements is read out as a light signal to a common output line. The light signal is amplified by a preamplifier and is processed by a differential amplifier to remove a noise component therefrom. The processed light signal is then output as a video signal to an amplifier.
In another photoelectric conversion apparatus disclosed in Japanese Laid-Open Patent Application No. 5-300309, electric charge from a light-sensitive section is transferred to an analog shift register and is then output as a video signal from an output buffer.
In a further photoelectric conversion apparatus disclosed in Japanese Laid-Open Patent Application No. 9-219823, electric charge from light-sensitive elements is processed and output as a video signal via a light-sensitive voltage generation circuit and a multiplexer. More specifically, light reflected from an original (document) is received and photoelectrically converted by a photoelectric conversion element array. An output signal from the photoelectric conversion element array is transferred as a sequential pixel signal to an analog shift register through an analog switch array. The sequential pixel signal is transferred to an output buffer and is then amplified and output as a video signal.
FIG. 8 is a block diagram showing a conventional photoelectric conversion apparatus CIS10.
The conventional photoelectric conversion apparatus CIS10 includes a photoelectric conversion element array 801, a switch array 802, an analog shift register 803 and an output buffer 804.
In the conventional photoelectric conversion apparatus CIS10, light reflected from an original (document) is received and photoelectrically converted by the photoelectric conversion element array 801. An output signal from the photoelectric conversion element array 801 is transferred as a sequential pixel signal to the analog shift register 803 via the analog switch array 802 in accordance with a timing signal TG. The sequential pixel signal is transferred to the output buffer 804 in accordance with pulse signals Φ1 and Φ2 and is then amplified and output as a video signal Vout.
In the above-described conventional photoelectric conversion apparatus, electric charge generated and stored in photoelectric conversion elements is subjected to noise removal and amplification and is then output as a video signal in synchronization with a driving signal. In addition, in the above-described conventional photoelectric conversion apparatus, when an original (document) or the like that is narrower than the main scanning length is read, all of the chips each having a photoelectric conversion function (photoelectric conversion elements) are driven.
Accordingly, outputs of chips that really should not be treated as an image will be processed as part of an ordinary video image. Therefore, wasteful electric power, e.g., driving power for photoelectric conversion chips that are located in an area other than an effective image area, is consumed.